<header>
    <nav>
        <style>
            nav ul {
                list-style-type: none;
                margin: 0;
                padding: 0;
                display: flex;
            }

            nav ul li {
                margin-right: 20px;
            }

            nav ul li a {
                text-decoration: none;
                color: #333;
                padding: 10px 15px;
                border-radius: 5px;
                transition: background-color 0.3s ease, color 0.3s ease;
            }

            nav ul li a:hover {
                background-color: #f0f0f0;
                color: #000;
            }
        </style>

        <ul>
            <li><a href="/">首页</a></li>
            <li><a href="/book">图书管理</a></li>
            <li><a href="/user">用户管理</a></li>
        </ul>
    </nav>
</header>